Charging small batteries?

MichaelJ

Greetings,

I have a small basic setup: one 135w panel, one 10a pwm controller, one 85ah sla battery. With initial help from members and mods, it works well with the small loads I use (led lights, recharge laptop).

My question, is there a way to limit the controller current to charge several sealed ups 12v batteries 7 - 15ah. I know that 7+amps would be a disaster, but wonder if it is possible to limit the amps, or do I need a small panel and controller.

Mike

BB.

Re: Charging small batteries?

Does the controller have adjustable set points (for sealed batteries, usually you wan no more than ~14.2 to 14.4 volts).

Also, you should find out if the batteries are GEL or something else. If they are AGM, they could probably take the higher current OK. You should monitor the battery temperature to make sure they do not overheat (I assume that the batteries are, sort of, expendable--Usually small batteries do not last much more than a year or so cycling).

If they are GEL batteries, you really do not want to give them more than 5% of rated current (0.05*7AH=0.35 amps). More than that, and you are probably looking at trashed batteries.

You could put a power resistor (or even an 6-12 watt automotive light bulb) in series with the panel to controller wiring to make the panel look smaller.

However, if you are planning on charging several batteries at a time, that probably is not a good idea. And if you are using GEL--You may want to consider AGM or flooded cell deep cycle. GELs are not great because they take so long to charge (i.e, the 5% max rate of charge).

-Bill

Cariboocoot

Re: Charging small batteries?

MichaelJ wrote: »

Greetings,

I have a small basic setup: one 135w panel, one 10a pwm controller, one 85ah sla battery. With initial help from members and mods, it works well with the small loads I use (led lights, recharge laptop).

My question, is there a way to limit the controller current to charge several sealed ups 12v batteries 7 - 15ah. I know that 7+amps would be a disaster, but wonder if it is possible to limit the amps, or do I need a small panel and controller.

Mike

The maximum output current can be limited by a series resistor, but it would require some experimenting.

Do you by any chance already have chargers specific to the batteries in question? If so, perhaps supplying the input requirements for them would be easier than trying to do an end-run around direct to the batteries. It's pretty easy to blow up small batteries with the wrong Voltage and/or current.

MichaelJ

Re: Charging small batteries?

Thanks for your replies.

I do have a set point for sealed batteries, and the batteries are just sealed fla. But given the options, the risk outweighs the benefit. And unless there is a way to limit amps and retain the voltage from the controller or the 85ah battery, I'm left with the option of a small panel.

Mike

PNjunction

Re: Charging small batteries?

MichaelJ wrote: »

I do have a set point for sealed batteries, and the batteries are just sealed fla. But given the options, the risk outweighs the benefit. And unless there is a way to limit amps and retain the voltage from the controller or the 85ah battery, I'm left with the option of a small panel.

Note that a "sealed" FLA is still a flooded battery, and wants to see a flooded voltage. On your morningstar CC, you'd remove the jumpers for flooded operation, even though the typical sealed maintenance-free FLA battery has no caps.

You would do the same thing for AGM batteries on the morningstar by removing the jumpers for flooded operation. What we're concerned most about here is the actual voltage. In Morningstar's case, "sealed" means about 14.1v, which is just right for gel - but we aren't using that. Flooded in a Morningstar pwm controller is about 14.4v, which is what you'd want for AGM or sealed FLA's. This one is easy to get confused on, so go by actual voltage ratings, and not necessarily the silkscreen label.

One option you have for small batteries to use with your large panel is to stop thinking ups-style agm's, which can only handle about 0.3C charge current max. Instead, look into small Hawker Cyclon monobloc agm's, or Odyssey agm's. The 18ah Odyssey PC-680 agm would do fine with your existing setup.

Hawker and Odysseys are TPPL agm's, and can basically handle as much current as you can throw at them as long as you have a CV charge controller, which your Morningstar is (albeit via pwm once into absorb). In fact, these batteries demand to see at LEAST 0.4C recharge as a MINIMUM if you take them to 50% DOD or lower, so for the 18ah PC680, that would be a minimum of 7.2A. Your 135 watt panel just meets this requirement.

Caution - once you charge an Odyssey or Hawker via solar in less than an hour, you may become hooked on agm's that can handle large charge currents! I know I did, and is a real option for those who have little solar insolation, but have the panel power to deal with these outstanding agm's.